Load control device having a low-power mode

ABSTRACT

A load control device for control of the power delivered from an AC power source to an electrical load comprises a power supply and a microprocessor that is able to operate the load control device in a low-power mode. The load control device may further comprise at least one visual indicator controlled by the microprocessor to provide visual feedback, where the microprocessor illuminates the visual indicator when the load is on and to turns the visual indicator off when the load is off during the low-power mode. The load control device may comprise a communication circuit coupled to the microprocessor for transmitting and/or receiving digital messages the microprocessor cause the communication circuit to draw less current from the power supply during the low-power mode. The microprocessor may operate in the low-power mode if the magnitude of a voltage of the power supply drops below a predetermined threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application ofcommonly-assigned, co-pending U.S. patent application Ser. No.12/369,395, filed Feb. 11, 2009, which is a continuation application ofU.S. patent application Ser. No. 11/480,146, filed Jun. 30, 2006, nowU.S. Pat. No. 7,546,473, issued Jun. 9, 2009, which claims priority fromU.S. Provisional Patent Application No. 60/695,784, filed Jun. 30, 2005,all entitled DIMMER HAVING A MICROPROCESSOR-CONTROLLED POWER SUPPLY, theentire disclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a two-wire load control device,specifically a two-wire dimmer switch having a microprocessor and apower supply for generating a direct-current (DC) voltage for poweringthe microprocessor, where the microprocessor is able to operate thedimmer switch in a low-power mode.

2. Description of the Related Art

A conventional two-wire dimmer has two connections: a “hot” connectionto an alternating-current (AC) power supply and a “dimmed hot”connection to the lighting load. Standard dimmers use one or moresemiconductor switches, such as triacs or field effect transistors(FETs), to control the current delivered to the lighting load and thusto control the intensity of the light. The semiconductor switches aretypically coupled between the hot and dimmed hot connections of thedimmer.

Smart wall-mounted dimmers may include a user interface typically havinga plurality of buttons for receiving inputs from a user and a pluralityof status indicators for providing feedback to the user. These smartdimmers typically include a microprocessor or other processing devicefor allowing an advanced set of control features and feedback options tothe end user. An example of a smart dimmer is disclosed in commonlyassigned U.S. Pat. No. 5,248,919, issued on Sep. 28, 1993, entitledLIGHTING CONTROL DEVICE, which is herein incorporated by reference inits entirety.

A simplified block diagram of a prior art two-wire dimmer 100 is shownin FIG. 1. The dimmer 100 has a hot terminal 102 connected to an ACvoltage source 104 and a dimmed hot terminal 106 connected to a lightingload 108 (e.g., an incandescent lamp). The dimmer 100 employs abidirectional semiconductor switch 110 coupled between the hot terminal102 and the dimmed hot terminal 106, to control the current through, andthus the intensity of, the lighting load 108. The semiconductor switch110 has a control input (or gate), which is connected to a gate drivecircuit 112. The input to the gate will render the semiconductor switch110 conductive or non-conductive, which in turn controls the powersupplied to the lighting load 108. The gate drive circuit 112 providescontrol inputs to the semiconductor switch 110 in response to commandsignals from a microprocessor 114.

The microprocessor 114 receives user inputs from a plurality of buttons116 and generates command signals to drive a plurality of light emittingdiodes (LEDs) 118 for visual feedback to the user of the dimmer 100. Azero-crossing detect circuit 120 determines the zero-crossing points ofthe AC source voltage from the AC power supply 104. A zero-crossing isdefined as the time at which the AC supply voltage transitions frompositive to negative polarity, or from negative to positive polarity, atthe beginning of each half-cycle. The zero-crossing information isprovided as an input to the microprocessor 114. The microprocessor 114generates the gate control signals to operate the semiconductor switch110 to thus provide voltage from the AC power supply 104 to the lightingload 108 at predetermined times relative to the zero-crossing points ofthe AC waveform.

In order to provide a DC voltage V_(CC) to power the microprocessor 114and other low-voltage circuitry, the dimmer 100 includes a cat-ear powersupply 122. A cat-ear power supply draws current only near thezero-crossings of the AC source voltage and derives its name from theshape of the current waveform that it draws from the AC voltage source.Because the dimmer 100 only has two terminals 102, 106 (i.e., it is atwo-wire dimmer), the power supply 122 must draw current through theconnected lighting load 108. In order for the power supply 122 to beable to draw sufficient current, the semiconductor switch 110 must benon-conductive so that a sufficient voltage is available across thepower supply. Thus, the semiconductor 110 cannot be turned on for theentire length of a half-cycle, even when the maximum voltage across thelighting load 108 is desired.

A simplified schematic diagram of the prior art cat-ear power supply 122is shown in FIG. 2. The cat-ear power supply is provided on the DC-sideof a bridge rectifier comprising diodes D202, D204, D206, D208, suchthat the cat-ear power supply is able to generate the DC voltage V_(CC).The DC voltage V_(CC) is produced across an energy storage capacitorC210 and has a magnitude that is appropriate to power the microprocessor114 and other low-voltage circuitry (e.g., approximately 5V_(DC)). Theside of the energy storage capacitor C210 that is connected to circuitcommon (i.e., the cathode) is also connected to an NPN transistor Q212and a PNP transistor Q214. A zener diode Z216 and a diode D218 areprovided in series between the DC voltage V_(CC) and the base of thetransistor Q214. The forward voltage drop of the diode D218 isapproximately the same as the emitter-base voltage of the transistorQ214. Accordingly, the magnitude of the DC voltage V_(CC) producedacross the energy storage capacitor C210 is limited to approximately thesame magnitude as the break-over voltage of the zener diode Z216, e.g.,5.1 volts.

The primary charging or energy-receiving circuit for the energy storagecapacitor C210 is through the transistor Q212 and a current limitingresistor 8220. When transistor Q214 is conductive, a voltage is producedacross a resistor R222, and thus the base-emitter junction of thetransistor Q212, causing the transistor Q212 to conduct. A resistor 8224maintains the base current needed to keep the transistor Q214conductive.

When the voltage across the power supply 122 reaches a certainmagnitude, a PNP transistor Q226 begins to conduct, causing thetransistor Q214, and thus the transistor Q212, to stop conducting. Azener diode Z228 and a resistor 8230 are connected in series between thebase of the transistor Q226 and the emitter of the transistor Q212. Aresistor 8232 is connected across the base-emitter junction of thetransistor Q226. The zener diode Z228 will begin to conduct when thevoltage at the base of the transistor Q226 exceeds the break-overvoltage of the zener diode (approximately 12V). When the voltage acrossthe resistor 8232 exceeds the required emitter-base voltage of thetransistor Q226, the transistor Q226 will begin to conduct. Thus, whenan appropriate voltage (e.g., approximately 16V) is produced across thepower supply 122, the transistor Q226 will begin to conduct, causing thetransistors Q212, Q214 to stop conducting, thus halting the charging ofthe energy storage capacitor C210. A capacitor C234 is coupled acrossthe resistor R232 to provide a time delay in the shut-off of thecharging of the energy storage capacitor C210. When the voltage acrossthe power supply 122 drops below the appropriate level (e.g.,approximately 16V), the transistor Q226 stops conducting and the energystorage capacitor C210 is able to charge again.

The prior art cat-ear power supply 122 has some disadvantages. First,the period of time that the energy storage capacitor C210 is able tocharge each half-cycle is set by the values of the chosen components ofthe power supply 122. If the power supply 122 is connected to an ACvoltage source when the capacitor C210 is uncharged, the power supply issusceptible to drawing the initial charging current at the peak of theAC voltage, which can produce a very large current in the chargingcircuit of the power supply 122, especially through the transistor Q212and the resistor R220. To prevent these parts from being damaged underthis condition, the transistor Q212 and resistor R220 must be physicallylarger, more costly parts than would be required if only operating undernormal conditions.

To ensure that the power supply 122 is able to draw enough current tomaintain its output voltage at all times, the semiconductor switch 110is turned off for at least a minimum off-time each half-cycle. Theproper operation of the dimmer 100 is constrained by a number ofworst-case operating conditions, such as high current draw by thelow-voltage circuitry, worst-case line voltage input (i.e. when the ACpower supply voltage is lower than normal), and worst-case loadconditions (such as the number and the wattage of the lamps, the type ofthe lamps, and variations in the operating characteristics of thelamps). The wattage of the lighting load 108 is particularly importantsince the AC voltage source 104 is coupled across the power supply 122and the lighting load in series, and thus, the impedance of the lightingload directly affects the voltage developed across the power supply andthe time required to charge the power supply. The impedance of alighting load will decrease as the rated wattage is increased, and viceversa. Thus, the worst-case time required to charge the power supply 122occurs when a low-wattage lamp is connected to the dimmer 100 since theimpedance of the load will be substantially higher and the voltageacross the power supply will be substantially lower with this type ofload. When considering the worst-case conditions, 40 W lamps are oftenused as the minimum load likely to be encountered.

By considering these worst-case conditions, the minimum off-time isdetermined by calculating the off-time that will guarantee that thepower supply 122 will charge fully for even the worst-case conditions.The resulting off-time generally ends up being a significant portion ofeach half-cycle and constrains the maximum light level of the attachedlighting load 108. However, these worst-case conditions are often notencountered in practice. Under typical conditions, the semiconductorswitch could be rendered conductive for a greater amount of time duringeach half-cycle in order to conduct current to the load for a greateramount of time. Accordingly, the lighting load 108 will reach a higherintensity that is closer to the intensity achieved when the full linevoltage is provided to the load.

Some prior art dimmers have held the minimum off-time constant under allconditions, and thus have suffered from a smaller dimming range thanwould otherwise be possible. Another prior art two-wire dimmer 300,which is shown in FIG. 3, monitors the internal power supply anddecreases conduction time of the semiconductor switch, if needed. Thetwo-wire dimmer 300 is able to provide the maximum possible lightintensity at high-end while simultaneously ensuring sufficient chargingtime for proper operation of an internal power supply, and hence, thedimmer. The dimmer 300 is described in greater detail in co-pending U.S.Pat. No. 7,242,150, issued Jul. 10, 2007, entitled DIMMER HAVING A POWERSUPPLY MONITORING CIRCUIT, which is incorporated herein by reference inits entirety.

Referring to FIG. 3, the two-wire dimmer 300 has two connections: a hotterminal 302 to an AC power supply 304 and a dimmed hot terminal 306 toa lighting load 308. To control the AC voltage delivered to the lightingload 308, two field-effect transistors (FETs) 310A, 310B are provided inanti-serial connection between the hot terminal 302 and the dimmed hotterminal 306. The first FET 310A conducts during the positive half-cycleof the AC waveform and the second FET 310B conducts during the negativehalf-cycle of the AC waveform. The conduction state of the FETs 310A,310B is determined by a microprocessor 314 that interfaces to the FETsthrough a gate drive circuit 312. The dimmer 300 also includes aplurality of buttons 316 for input from a user and a plurality of LEDs318 for visual feedback to the user. The microprocessor 314 determinesthe appropriate dimming level of the lighting load 308 from the inputsfrom the buttons 316. A zero-crossing detect circuit 320 receives the ACsupply voltage through diode 321A in the positive half-cycles andthrough diode 321B in the negative half-cycles and provides a controlsignal to the microprocessor 314 that identifies the zero-crossings ofthe AC supply voltage.

The dimmer 300 further includes a power supply 322 to power themicroprocessor 314 and the other low-voltage circuitry. The power supply322 is only able to charge when the FETs 310A, 310B are both turned off(i.e., they are non-conducting) and there is a sufficient voltagepotential across the dimmer. The power supply 322 is coupled to an inputcapacitor 324 and an output capacitor 326. The output capacitor 326holds the output of the power supply V_(CC) at a substantially constantDC voltage to provide power for the microprocessor 314. The input of thepower supply 322 is coupled to the hot terminal 302 and the dimmed hotterminal 306 through the two diodes 321A, 321B, such that the inputcapacitor 324 charges during both the positive and negative half-cycles.

The dimmer 300 also includes a voltage divider that comprises tworesistors 328, 330 and is coupled between the input of the power supply322 and circuit common. The voltage divider produces a sense voltageV_(S) at the junction of the two resistors 328, 330. The sense voltageV_(S) is provided to the microprocessor 314 to monitor the voltage levelat the input of the power supply 322. The microprocessor 314 preferablyincludes an analog-to-digital converter (ADC) for sampling the value ofthe sense voltage V_(S). The microprocessor 314 monitors the sensevoltage V_(S) and decreases the conduction times of the FETs 310A, 310Bwhen the sense voltage V_(S) drops below a first predetermined voltagethreshold V₁. Further, the microprocessor 314 increases the conductiontimes of the FETs 310A, 310B when the sense voltage then rises above asecond predetermined voltage threshold V₂, greater than the firstthreshold V₁. Alternatively, if the microprocessor does not include anADC, the dimmer 100 could include a hardware comparison circuit,including one or more comparator integrated circuits, to compare thesense voltage with the first and second voltage thresholds and thenprovide a logic signal to the microprocessor 314.

By monitoring the input of the power supply 322, the microprocessor 314of the dimmer 300 is able to determine when the input voltage hasdropped to a level that is inappropriate for continued charging of theinput capacitor 324. For example, if the sense voltage V_(S) falls belowthe first voltage threshold V₁, then the capacitor 324 needs a greatertime to properly charge and the on-times of the FETs 310A, 310B aredecreased. On the other hand, if the sense voltage V_(S) remains abovethe first voltage threshold V₁, the input capacitor 324 is able toproperly charge each half-cycle.

Thus, the microprocessor 314 continuously monitors the voltage on theinput capacitor 324 and automatically decreases the conduction times ofthe FETs 310A, 310B when the voltage falls to a level that will notguarantee proper operation of the power supply 322. The dimmer 300 isable to provide the maximum possible conduction times of the FETs 310A,310B at high end (i.e., maximum light intensity) while simultaneouslyensuring sufficient charging time for proper operation of the powersupply 322.

However, the dimmer 300 of FIG. 3 requires that the microprocessor 314include an ADC or that a hardware comparison circuit be included betweenthe power supply 322 and the microprocessor. Also, the dimmer 300 is notable to control the power supply 322 directly, but operates the FETs310A, 310B in order to indirectly control the time during which thepower supply draws current.

Thus, there exists a need for a simple cat-ear power supply for a dimmerthat is operable to be monitored and directly controlled by amicroprocessor, specifically to control the time period that the powersupply draws current and to control the conduction time of thesemiconductor switch in response to the operation of the power supply,without the need for an ADC or a complex hardware comparison circuit.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a load controldevice for control of the power delivered from an AC power source to anelectrical load comprises: (1) a controllably conductive device adaptedto be coupled between the AC power source and the electrical load forcontrolling the power delivered to the load; (2) a microprocessorcoupled to the controllably conductive device for controlling thecontrollably conductive device; (3) at least one visual indicatorcontrolled by the microprocessor to provide visual feedback; and (4) apower supply adapted to draw current from the AC power source throughthe electrical load for generating a DC voltage across an energy storagecapacitor for powering the microprocessor and the visual indicator. Themicroprocessor is able to operate the load control device in a low-powermode during which the microprocessor illuminates the visual indicatorwhen the load is on and to turns the visual indicator off when the loadis off.

According to another embodiment of the present invention, a load controldevice for control of the power delivered from an AC power source to anelectrical load comprises: (1) a controllably conductive device adaptedto be coupled between the AC power source and the electrical load forcontrolling the power delivered to the load; (2) a microprocessorcoupled to the controllably conductive device for controlling thecontrollably conductive device; (3) a communication circuit coupled tothe microprocessor for transmitting and/or receiving digital messages;and (4) a power supply adapted to draw current from the AC power sourcethrough the electrical load for generating a DC voltage across an energystorage capacitor for powering the microprocessor and the communicationcircuit. The microprocessor is able to operate the load control devicein a low-power mode during which the microprocessor causes thecommunication circuit to draw less current from the energy storagecapacitor.

According to another embodiment of the present invention, a load controldevice for control of the power delivered from an AC power source to anelectrical load comprises: (1) a controllably conductive device adaptedto be coupled between the AC power source and the electrical load forcontrolling the power delivered to the load; (2) a microprocessorcoupled to the controllably conductive device for controlling thecontrollably conductive device; (3) a power supply adapted to drawcurrent from the AC power source through the electrical load forgenerating a DC voltage across an energy storage capacitor for poweringthe microprocessor and the LED; and (4) a load circuit drawing currentfrom the energy storage capacitor of the power supply. Themicroprocessor is operable to cause the load circuit to draw lesscurrent if the magnitude of a voltage of the power supply drops below apredetermined threshold.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a prior art two-wire dimmer;

FIG. 2 is a simplified schematic diagram of a cat-ear power supply ofthe dimmer of FIG. 1;

FIG. 3 is a simplified block diagram of another prior art two-wiredimmer;

FIG. 4 is a simplified block diagram of a two-wire dimmer according tothe present invention;

FIG. 5A is a simplified schematic diagram of a cat-ear power supplyaccording to the present invention;

FIG. 5B is a simplified schematic diagram of a cat-ear power supplyincluding a half-wave rectifier bridge according to the presentinvention;

FIG. 5C is a simplified schematic diagram of a cat-ear power supplyincluding a transistor in series with a boot-strap resistor according tothe present invention;

FIG. 6A shows a flowchart of the normal operation process of amicroprocessor of the dimmer of FIG. 4;

FIG. 6B shows a flowchart of a power supply control/monitor routine ofthe process of FIG. 6A;

FIG. 6C shows a flowchart of a dimming range control routine of theprocess of FIG. 6A; and

FIG. 7 shows a flowchart of the startup routine of the microprocessor ofthe dimmer of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 4 is a simplified block diagram of a two-wire dimmer 400 accordingto the present invention. The dimmer 400 includes many similar blocks asthe dimmer 100 of FIG. 1, which have the same function as describedpreviously. However, those components of the dimmer 400 that differ fromthe prior art dimmer 100 will be described in greater detail below.

The dimmer 400 includes a controllably conductive device, e.g., abidirectional semiconductor switch 410, that is adapted to be coupled inseries electrical connection between an AC power source 404 and alighting load 408. The bidirectional semiconductor switch 410 may beimplemented as, for example, a triac, a field effect transistor (FET) oran insulated gate bipolar transistor (IGBT) in a bridge rectifier, twoFETs or IGBTs in anti-series connection, or any other suitable type ofsemiconductor switch. The dimmer 400 further comprises a microprocessor414 for driving the bidirectional semiconductor switch 410 via a gatedrive circuit 412. The microprocessor 414 may be implemented as anysuitable controller, such as, for example, a programmable logic device(PLD), a microcontroller, an application specific integrated circuit(ASIC), or a field programmable gate array (FPGA).

The microprocessor 414 receives inputs from a zero-crossing detectorcircuit 420 and a plurality of buttons 416 and controls a plurality ofLEDs 418. The microprocessor 414 is operable to illuminate one of theLEDs 418 brightly to a first intensity. When the lighting load 108 isoff, the microprocessor 414 may illuminate the LEDs 418 dimly to asecond intensity less than the first intensity to provide a nightlightfeature. One of the LEDs 418 may be illuminated to a third intensity(between the first and second intensities) to display a target intensityto which the microprocessor 414 will control the lighting load 108 whenthe lighting load is turned back on. The nightlight feature is describedin greater detail in commonly-assigned U.S. Pat. No. 5,399,940, issuedMar. 21, 1995, entitled LIGHTING INDICATING DEVICE HAVING PLURALILLUMINATING ELEMENTS WITH ALL SUCH ELEMENTS BEING ILLUMINATED WITH ONEBEING GREATER THAN THE OTHERS, the entire disclosure of which is herebyincorporated by reference

A cat-ear power supply 422 generates a DC voltage V_(CC) for poweringthe microprocessor 414. The microprocessor 414 is coupled to the cat-earpower supply through a port 424 and is operable to monitor the status ofthe power supply (i.e., whether the power supply is fully charged) andto control the operation of the power supply.

The dimmer 400 also includes a communication circuit 426 to transmit andreceive messages with other control devices in a lighting controlsystem. The communication circuit 426 is coupled to a communicationslink, for example, a wired serial control link, a power-line carrier(PLC) communication link, or a wireless communication link, such as aninfrared (IR) or a radio frequency (RF) communication link. For example,the communication circuit 426 may comprise an RF communication circuit(e.g., an RF transmitter, an RF receiver, or an RF transceiver) fortransmitting and/or receiving RF signals. The microprocessor 414 may beoperable to control the bidirectional semiconductor switch 410 inresponse to the digital messages received via the RF signals. The RFcommunication circuit is able to be put in a sleep mode (i.e., low-powermode) to conserve power. During the sleep mode, the RF communicationcircuit is operable to wake up periodically to sample (e.g., listen) forRF energy at a sampling period T_(SAMPLE). Each time that the RFtransceiver wakes up, additional power is consumed by the RF transceiver(since the RF transceiver is fully powered when awake).

Examples of RF load control devices are described in greater detail incommonly-assigned U.S. Pat. No. 5,982,103, issued Nov. 9, 1999, and U.S.Pat. No. 7,362,285, issued Apr. 22, 2008, both entitled COMPACT RADIOFREQUENCY TRANSMITTING AND RECEIVING ANTENNA AND CONTROL DEVICEEMPLOYING SAME, and U.S. patent application Ser. No. 13/415,537, filedMar. 8, 2012, entitled LOW-POWER RADIO-FREQUENCY RECEIVER, the entiredisclosures of which are hereby incorporated by reference. An example ofan IR lighting control system is described in commonly assigned U.S.Pat. No. 6,300,727, issued Oct. 9, 2001, entitled LIGHTING CONTROL WITHWIRELESS REMOTE CONTROL AND PROGRAMMABILITY, the entire disclosure ofwhich is hereby incorporated by reference.

FIG. 5A is a simplified schematic diagram of the cat-ear power supply422 according to the present invention. The cat-ear power supply 422 isprovided inside of a full-wave bridge rectifier comprising diodes D502,D504, D506, D508, such that the cat-ear power supply is able to producea DC voltage V_(CC) across an energy storage element, for example, anenergy storage capacitor C510. The rectifier bridge allows the cat-earpower supply 422 to draw current in both half-cycles of the AC sourcevoltage. The energy storage capacitor preferably has a capacitance ofapproximately 680 μF.

Alternatively, the cat-ear power supply 422 could include a half-wavebridge rectifier, for example, comprising only diode D508, i.e., thediodes D502, D504, D506 would not be provided, as shown in FIG. 5B. Thehalf-wave rectifier bridge comprising only one diode D508 would allowthe cat-ear power supply 422 to charge in only the positive or thenegative half-cycles and thus only once per line cycle.

The cat-ear power supply 422 includes a passive charging orenergy-receiving circuit comprising a “boot-strap” resistor R512. Theresistor R512 allows the energy storage capacitor C510 to begin chargingbefore the microprocessor 414 is powered up and running, such that theenergy storage capacitor C510 is only charged by the current flowingthrough the resistor R512 and the impedance of the lighting load 408.The resistor R512 preferably has a resistance of 151 a which is suitablylow enough to ensure sufficient current is available to bring themicrocontroller out of the internal low-voltage reset mode. The currentthrough the resistor R512 provides sufficient charge on the energystorage capacitor C510 to bring the microprocessor 414 out of aninternal low-voltage reset mode (e.g., when voltage supply input to themicroprocessor rises above approximately 3.75V). During the time whenthe energy storage capacitor C510 is charging through the boot-strapresistor R512, the majority of the current drawn from the power supply422 (i.e., drawn by the microprocessor 414 and the other low-voltagecircuitry) is minimal since the microprocessor is unpowered or in resetmode. The energy storage capacitor C510 charges through the boot-strapresistor R512 until the microprocessor 414 is running and able tocontrol the power supply 422. The boot-strap resistor R512 is also sizedto be suitably large enough in impedance so that during normaloperation, the power dissipation of the resistor is minimized.

Once powered, the microprocessor 414 can enable an active charging orenergy-receiving circuit for the energy storage capacitor C510 throughan NPN transistor Q514 (e.g., part number MJD47T4 manufactured by OnSemiconductor) and a resistor R516. The resistor R516 has a lowresistance (preferably 12Ω), which provides a charging current throughthe energy storage capacitor C510 of a much greater magnitude than thecharging current through the passive charging circuit comprising theresistor R512, thus allowing the energy storage capacitor C510 to chargeat a greater rate, i.e., with a smaller time constant. Themicroprocessor 414 is coupled to the base of a PNP transistor Q518(e.g., part number MMBTA92 manufactured by On Semiconductor) through aresistor R520 (preferably having a resistance of 4.7 kΩ). When theenergy storage capacitor C510 is charging through the resistor R512during start up, the port 424 of the microprocessor 414 that isconnected to the resistor R520 is maintained as a high impedance and thetransistor Q514 is non-conductive.

Upon coming out of reset mode, the microprocessor 414 measures thefrequency of, and synchronizes to, the AC voltage supply 404 by means ofthe zero-crossing detect circuit 420 and the internal clock of themicroprocessor. After synchronizing with the AC voltage supply 404, themicroprocessor 414 can enable the active charging circuit by pulling theport 424 low and thereby pulling down the base of the transistor Q518.Thus, a voltage is produced across a resistor R522 and the emitter-basejunction of the transistor Q518 allowing current flow through thetransistor Q518 and an emitter resistor R524. The resistors R522, R524preferably have resistances of 10 kΩ and 510Ω, respectively. The currentflow through the transistor Q518 produces a voltage across a resistorR526 coupled across the base-emitter junction of the transistor Q514 andprovides base current for the transistor Q514. This enables the activecharging circuit of the energy storage capacitor C510, allowing thecharging current for the energy storage capacitor C510 to flow throughthe transistor Q514 and the resistor R516. The current through thetransistor Q514 is limited by the resistor R516 and a zener diode Z528(preferably having a break-over voltage of 3.3V, e.g., part numberMMSZ4684ET1 manufactured by On Semiconductor). A capacitor C530 iscoupled across the resistor R526 and provides some time delay in theenabling of the active charging circuit. Preferably, the resistor R526has a resistance of 10 kΩ and the capacitor C530 has a capacitance of0.33 μF.

The power supply 422 further includes a hardware shut-off circuit havinga PNP transistor Q536, a resistor R532, and a zener diode Z534. Theresistor R532 (preferably having a resistance of 1 kΩ) and the zenerdiode Z534 are coupled in series across the energy storage capacitorC510, with the anode of the zener diode connected to circuit common. ThePNP transistor Q536 (e.g., part number MBT3906DW1T1 manufactured by OnSemiconductor) is coupled between the DC voltage V_(CC) and the base ofthe transistor Q518. The base of the transistor Q536 is connected to thejunction of the resistor R532 and the zener diode Z534. The zener diodeZ534 preferably has a break-over voltage of 4.7V (e.g., part numberMMSZ4688ET1 manufactured by On Semiconductor), such that when thevoltage across the energy storage capacitor C510 reaches approximately5.2V (i.e., the DC voltage V_(CC) is at an appropriate level), currentwill flow through the zener diode Z534 and the resistor R532, producinga voltage across the resistor. Thus, the transistor Q536 will begin toconduct, pulling the base of the transistor Q518 up to the DC voltageV_(CC). This overrides the control signal from the port 424 of themicroprocessor 414 and disables the active charging circuit through thetransistor Q514 and the resistor R516.

The microprocessor 414 is operable to monitor the voltage at the base ofthe transistor Q518 to determine if the energy storage capacitor C510has fully charged. By briefly changing the port 424 from beingconfigured as an output to being configured as an input, themicroprocessor 414 can periodically check to see if the base of thetransistor Q518 is being pulled up to the DC voltage V_(CC) by thetransistor Q536. A capacitor C538 is provided from the DC voltage V_(CC)to the base of the transistor Q518 and preferably has a capacitance of0.01 g. During the times that the port 424 has been changed to an inputto monitor the power supply 422, the capacitor C538 holds the voltage atthe base of the transistor Q518 at a level appropriate to keep thetransistor Q518 in the conductive state if the charging of the energystorage capacitor C510 has not yet finished.

The microprocessor 414 is adapted to control the time period when theactive charging circuit through the transistor Q514 is enabled eachhalf-cycle of the AC voltage source 404. In order to limit this chargingtime to the beginning portion of each half-cycle, the microprocessor 414only enables the active charging circuit at a predetermined time after azero-crossing has been detected by the zero-crossing detect circuit 420.In this way, the active charging circuit is never enabled when the ACvoltage is at its peak value. Accordingly, the transistor Q514 and theresistor R516 are never operated outside of their safe operating area,and do not need to be large, expensive parts as were required in theprior art cat-ear power supply 122 of FIG. 2.

In response to the time that is required to charge the power supply 422,the microprocessor 414 is operable to change the dimming range of thedimmer. By default, the dimmer 400 begins operating with a normaldimming range that has been determined by considering worst-case lineconditions and load conditions. For example, the worst-case loadcondition for the power supply 422 assumes a 40 W lamp as the lightingload. The microprocessor 414 can change the dimming range of dimmer 400to a maximum dimming range to provide a greater high-end intensity ofthe attached lighting load than the normal dimming range. Themicroprocessor 414 can also change the dimming range back to the normaldimming range in response to operating conditions.

The microprocessor 414 preferably includes a timer such that themicroprocessor is able to record the time required to charge the powersupply 422 each half-cycle. The microprocessor records the time fromwhen the active charging circuit is enabled to when the port 424 ispulled high by the transistor Q536 of the hardware shut-off circuit. Ifthis time is below a predetermined threshold for a number of consecutivehalf-cycles, it is assumed that the energy storage capacitor C510 iseasily able to charge each half-cycle and the microprocessor 414 isprogrammed to increase the dimming range of the dimmer 400 to themaximum dimming range, such that the high-end has a greater intensity.Since the average current draw of the power supply 422 is greatlydependent on the impedance of the connected lighting load, the dimmer400 will generally tend to continue operating with either the normaldimming range or the maximum dimming range, without changing between theranges, until the connected lighting load is changed to a differentwattage. Since the load impedance changes as the dimmer 400 changes theintensity of the lighting load 408 (i.e., as the light level isincreased, the impedance of the lighting load will increase), themicroprocessor 414 preferably monitors the time required to charge theenergy storage capacitor C510 at or near high-end since this is when thepower supply 422 will draw the worst-case charging current.

The microprocessor 414 is also capable of disabling the active chargingcircuit by pulling the port 424 high before the hardware shut-offcircuit disables the active charging circuit. If a predetermined timeelapses (from when the active charging circuit is enabled) before thetransistor Q536 shuts off the active charging circuit, themicroprocessor 414 will preferably override the hardware shut-offcircuit to protect the transistor Q514 and the resistor R516 frompotential damage, i.e., as the voltage across the dimmer increases, thecurrent through, and the power dissipation of, the transistor Q514 andthe resistor R516 will increase. The predetermined time preferablycorresponds to a time after which the voltage across the dimmer is greatenough to pose a potential hazard to the susceptible parts of the powersupply 422, i.e., the transistor Q514 and the resistor R516. The energystorage capacitor C510 can potentially require greater amounts of timeto charge: (1) during startup of the power supply 422; (2) if the powerrequirements of the microprocessor 414 and other low-voltage circuitryare greater than normal; or (3) if the energy storage capacitor is notable to charge during a certain half-cycle.

The microprocessor 414 is also able to control the loads of the powersupply 422, i.e., the gate drive circuit 412, the LEDs 418, and thecommunication circuit 426 (i.e., load circuits). If the microprocessor414 detects that the energy storage capacitor C510 does not have enoughtime to charge during each half-cycle, the microprocessor 414 canoptionally cause some of the loads of the power supply to draw lesscurrent by, for example, turning off or dimming the LEDs 418, turningoff the semiconductor switch 410, disabling the communication circuit426, or placing the communication circuit in an idle mode.Alternatively, the microprocessor 414 could increase the sampling periodT_(SAMPLE), such that the RF communication circuit wakes up less oftento sample for RF energy and thus consumes less power. Also, during thestartup of the power supply 422, the microprocessor 414 does not enablethe loads of the power supply until after a predetermined number ofhalf-cycles to allow the DC voltage V_(CC) provided by the energystorage capacitor C510 to achieve a stable value.

The power supply 422 may also include an additional semiconductorswitch, for example, a NPN transistor Q540 (as shown in FIG. 5C), forselectively switching the boot-strap resistor R512 out of the circuitafter startup of the power supply, i.e., when the boot-strap resistor isno longer needed. The base of the transistor Q540 is coupled to anoutput port 542 of the microprocessor 414 through a resistor R544.Accordingly, the microprocessor 414 is operable to render the transistorQ540 non-conductive to disable the passive energy-receiving circuitcomprising the boot-strap resistor R512. The base of the transistor Q540is also coupled to a resistor R546. Before the microprocessor 414 ispowered, a current flows through the resistor R546 into the base of thetransistor Q540, such that the transistor Q540 allows the energy storagecapacitor C510 to charge through the boot-strap resistor R512.

FIG. 6A shows a flowchart of the normal operation process of themicroprocessor 414 for controlling the power supply 422 of the dimmer400. This process is performed each half-cycle. The process begins eachhalf-cycle at a zero-crossing of the AC voltage at step 600, and thenexecutes in sequence a power supply control/monitor routine 602 and adimming range control routine 604.

FIG. 6B shows a flowchart of the power supply control/monitor routine602 in greater detail. At step 605, a “turn-on” timer is initialized,for example, to 150 μsec, and is started in a decrementing operation.The turn-on timer determines the time between a zero-crossing and whenthe active charging circuit is enabled. If the turn-on timer has notelapsed (i.e., has not decreased to zero) at step 606, the process loopsuntil the turn-on timer has elapsed, at which time a “turn-off” timer isstarted at step 608 and decreases in value with respect to time. Theturn-off timer is initialized, for example, to 400 μsec, and is used tooverride the hardware shut-off circuit comprising transistor Q536 if theenergy storage capacitor C510 does not charge fully before the turn-offtimer elapses (i.e., decreases to zero).

At step 610, port 424 of the microprocessor 414 is configured as anoutput, and then, the port 424 is pulled low at step 612, thus enablingthe active charging circuit and causing the energy storage capacitorC510 to begin charging (i.e., storing energy) at a greater rate, i.e.,with a smaller time constant. Next, the microprocessor waits for a timet_(WAIT) (which is preferably 100 μsec to 200 μsec) at step 614. Now,the microprocessor 414 checks the voltage at the port 424 by firstconfiguring the port as an input at step 616 and then reading the portat step 618. The voltage at the port 424 will either be low (i.e., at orabout zero volts) if the energy storage capacitor C510 has not finishedcharging, or high (i.e., at or about V_(CC)) if the energy storagecapacitor C510 is sufficiently charged and the transistor Q536 isconducting. Since the microprocessor 414 can only cease driving the port424 for short, infrequent periods of time to prevent disabling theactive charging circuit, the wait operation at step 614 allows themicroprocessor 414 to periodically monitor the voltage at port 424 at anappropriate interval of time.

At step 620, if the port 424 is high, then the turn-off timer is stoppedat step 622, the port 424 is configured as an output at step 624, andthe port is pulled high at step 626. The process then exits. If at step620 the port 424 is still low, a determination is made at step 628 as towhether the turn-off time has expired. If not, the process loops aroundto enable the active charging circuit and then to monitor the port 424again. If the turn-off timer has expired at step 628, the activecharging circuit is enabled at steps 624 and 626 and then the processexits.

FIG. 6C shows a flowchart of the dimming range control routine 604 ingreater detail. At step 630, a charging time, t_(CHARGE), of the powersupply 422 for the present half-cycle is determined from the final valueof the turn-off timer. For example, if the original value of theturn-off timer is 400 μsec and the final value of the turn-off timer is150 μsec, the charging time t_(CHARGE) is 250 μsec. If at step 632, thecharging time t_(CHARGE) is less than a threshold, t_(TH), then themicroprocessor 414 attempts to change the dimmer 400 to the maximumdimming range. If the charging time t_(CHARGE) is above the thresholdt_(TH) at step 632, the microprocessor 414 will attempt to change thedimmer 400 to the normal dimming range. A variable K and a variable Mare used to count the number of consecutive half-cycles that thecharging time t_(CHARGE) is below the threshold t_(TH), or above thethreshold t_(TH), respectively. Note that the variables K and M arepreferably initialized to zero. The variables K and M are incrementeduntil the variables reach maximum values, K_(MAX) and M_(MAX),respectively. Preferably, the maximum values K_(MAX) and M_(MAX) areboth 3.

At step 634, if the variable M is greater than zero (i.e., the chargingtime t_(CHARGE) was above the threshold t_(TH) during the previoushalf-cycle), then the variable M is reset to zero (i.e., M equals zero)at step 636 and the variable K is incremented by one at step 638. If thevariable M is not greater than zero at step 634, the process simplymoves to step 638. If the variable K is equal to K_(MAX) at step 640,the charging time t_(CHARGE) has been above the threshold t_(TH) for theappropriate number of consecutive times and the dimming range isaccordingly changed to the maximum dimming range at step 642. However,if the variable K is not equal to K_(MAX) at step 640, the dimming rangeis not changed and the process exits.

If the charging time t_(CHARGE) is above the threshold t_(TH) at step632, the microprocessor 414 uses a similar process in steps 644, 646,648, 650 to determine if the dimmer 400 should change to the normaldimming range at step 652.

FIG. 7 shows a flowchart of the startup routine of the microprocessor414. The process begins when the microprocessor comes out of reset modeat step 702. At step 704, the microprocessor 414 maintains the port 424at high impedance to keep the active charging circuit through transistorQ514 disabled. The microprocessor 414 measures the frequency of the ACsource voltage and synchronizes to this frequency at step 706. At step708, the variables K and M (that are used in the dimming range controlroutine 604) and a variable ZC_CNT are initialized to zero. The variableZC_CNT is used by the startup routine to count the zero-crossings of theAC voltage supply 404 after startup.

Next, the microprocessor 414 executes the power supply control/monitorroutine 602 (as shown in FIG. 6B) for a number, ZC_(MAX), of consecutivehalf-cycles to allow the power supply 422 to regulate the voltage acrossthe energy storage capacitor C510 to a specified level. At step 710, theprocess waits until a zero-crossing is detected, and then the powersupply control/monitor routine 602 is executed. At step 712, if thevariable ZC_CNT is less than or equal to the number ZC_(MAX), then thevariable ZC_CNT is incremented by one at step 714 and the process loopsto wait for the next zero-crossing at step 710. If the variable ZC_CNTis greater than the number ZC_(MAX) at step 656, the microprocessor 414then begins driving the semiconductor switch 410 to provide power to thelighting load 408, turns on the LEDs 418, and begins communicating viathe communication circuit 426 at step 716. Next, the startup routineexits.

While the present invention has been primarily discussed operating in aclosed loop mode in which the microprocessor 414 is able to monitor thepower supply 422, the microprocessor may also operate in an open loopmode. The microprocessor 414 could simply turn on (i.e., enable) theactive charging circuit each half-cycle and allow the hardware shut-offcircuit to turn off (i.e., disable) the active charging circuit.Alternatively, the microprocessor 414 could turn off the active chargingcircuit of the power supply 422 at a predetermined time after the activecharging circuit is turned on, rather than monitoring the power supplyin order to turn off the active charging circuit.

In addition, the microprocessor 414 may alternatively be operable tomonitor the magnitude of a voltage of the power supply 422 to determineif the capacitor C510 has enough time to sufficiently charge rather thanmeasuring the time required to charge the capacitor C510 each half-cycleand determining if the time required to charge the capacitor C510 isbelow a predetermined threshold for a number of consecutive half-cycles.For example, the microprocessor 414 may monitor the DC voltage V_(CC)across the capacitor C510 or another operating voltage of the powersupply 422. The microprocessor 414 is operable to cause the loads of thepower supply 422 (i.e., the gate drive circuit 412, the LEDs 418, andthe communication circuit 426) to draw less current if the magnitude ofthe DC voltage V_(CC) across the capacitor C510 of the power supplydrops below a predetermined threshold.

While the present invention has been described with reference to thelighting load 108 (shown as an incandescent lamp in FIG. 1), thelighting load could also comprise other types of lighting loads, suchas, for example, screw-in light-emitting diode (LED) light sourceshaving integral LED drivers, screw-in compact fluorescent lamps havingintegral ballast circuits, halogen lamps, electronic low-voltagelighting loads, and magnetic low-voltage lighting loads, and other typesof electrical loads, such as, for example, motor loads. In addition, theconcepts of the present invention could be applied to an electronicswitch for simply toggling an electrical load on and off.

With some types of lighting loads, such as the screw-in LED lightsources and the screw-in compact fluorescent lamps, the magnitude of thecharging current of the power supply 422 conducted through the load maybe great enough to cause either the LED driver or the ballast circuit toilluminate the controlled LED light source or fluorescent lamp to alevel that is perceptible by the human eye when the light source shouldbe off. Accordingly, the microprocessor 414 may be operable to cause thedimmer 400 enter a low-power mode in response to a user executing anadvanced programming mode of the dimmer, i.e., in response to one ormore actuations of the buttons 416. In the low-power mode, themicroprocessor 414 may disable one or more of the loads of the powersupply 422 (i.e., the gate drive circuit 412, the LEDs 418, and thecommunication circuit 426) to decrease the magnitude of the currentconducted through the lighting load 108 when the lighting load is off.For example, the microprocessor 414 may be operable to turn off the LEDs418, such that the dimmer 400 does not provide the nightlight featurewhen the lighting load 108 is off. Further, the microprocessor 414 maybe operable to disable the RF communication circuit when the lightingload 108 is off, for example, by controlling an enable pin of anintegrated circuit (IC) of the RF communication circuit or by renderingnon-conductive a controllable switch (e.g., a transistor) that iselectrically coupled between the DC voltage V_(CC) and the RFcommunication circuit. Alternatively, the microprocessor 414 couldincrease the sampling period T_(SAMPLE), such that the RF communicationcircuit wakes up less often to sample for RF energy and thus consumesless power.

Although the word “device” has been used to describe the load controldevice of the present invention and the elements of the load controldevice, it should be noted that each “device” described herein need notbe fully contained in a single enclosure or structure. For example, thedimmer 400 may comprise a plurality of buttons in a wall-mountedenclosure and a processor that is included in a separate location. Also,one “device” may be contained in another “device”.

Additionally, the circuit diagrams shown in the figures and described inthe text are an example of the invention and are not the onlyimplementations possible. As appreciated by a person of ordinary skillin the art, component, software, and circuit substitutions andalterations may be made to the present invention without limitationexcept as identified by the appended claims.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A load control device for control of the power delivered from an ACpower source to an electrical load, the load control device comprising:a controllably conductive device adapted to be coupled between the ACpower source and the electrical load for controlling the power deliveredto the load; a microprocessor coupled to the controllably conductivedevice for controlling the controllably conductive device; at least onevisual indicator controlled by the microprocessor to provide visualfeedback; and a power supply adapted to draw current from the AC powersource through the electrical load for generating a DC voltage across anenergy storage capacitor for powering the microprocessor and the visualindicator; wherein the microprocessor is able to operate the loadcontrol device in a low-power mode during which the microprocessorilluminates the visual indicator when the load is on and to turns thevisual indicator off when the load is off.
 2. The load control device ofclaim 1, further comprising: a button for receiving a user input;wherein the control circuit is able to operate the load control devicein the low-power mode in response to an actuation of the button.
 3. Theload control device of claim 2, wherein the microprocessor is operableto cause the load control device to enter the low-power mode using anadvanced programming mode of the load control device.
 4. The loadcontrol device of claim 1, wherein the load circuit comprises aplurality of visual indicators controlled by the microprocessor toprovide visual feedback; wherein the microprocessor is operable toilluminate at least one of the visual indicators when the load is on andto turn off all of the visual indicators when the load is off whenoperating in the low-power mode
 5. The load control device of claim 1,wherein, when not in the low-power mode, the microprocessor is operableto illuminate the visual indicator to a first intensity when the load ison and to illuminate the visual indicator to second intensity less thanthe first intensity when the load is off.
 6. The load control device ofclaim 1, wherein the load control device comprises a dimmer forcontrolling the power delivered to a lighting load.
 7. The load controldevice of claim 1, wherein the power supply comprises a transistor forcontrollably storing energy in the energy storage capacitor, themicroprocessor operatively coupled to the transistor for controlling thetransistor.
 8. A load control device for control of the power deliveredfrom an AC power source to an electrical load, the load control devicecomprising: a controllably conductive device adapted to be coupledbetween the AC power source and the electrical load for controlling thepower delivered to the load; a microprocessor coupled to thecontrollably conductive device for controlling the controllablyconductive device; a communication circuit coupled to the microprocessorfor transmitting and/or receiving digital messages; and a power supplyadapted to draw current from the AC power source through the electricalload for generating a DC voltage across an energy storage capacitor forpowering the microprocessor and the communication circuit; wherein themicroprocessor is able to operate the load control device in a low-powermode during which the microprocessor causes the communication circuit todraw less current from the energy storage capacitor.
 9. The load controldevice of claim 8, wherein the communication circuit comprises an RFcommunication circuit adapted to be coupled to an RF communication link.10. The load control device of claim 9, wherein the microprocessor isoperable to cause the load control device to enter the low-power modeusing an advanced programming mode of the load control device.
 11. Theload control device of claim 9, wherein the microprocessor is operableto increase the sampling period of the RF communication circuit, suchthat the RF communication circuit wakes up less often to sample for RFenergy.
 12. The load control device of claim 8, further comprising: abutton for receiving a user input; wherein the microprocessor isoperable to operate the load control device in a low-power mode inresponse to an actuation of the button.
 13. The load control device ofclaim 12, wherein the microprocessor is operable to cause the loadcontrol device to enter the low-power mode using an advanced programmingmode of the load control device.
 14. The load control device of claim 8,wherein the load control device comprises a dimmer for controlling thepower delivered to a lighting load.
 15. The load control device of claim8, wherein the power supply comprises a transistor for controllablystoring energy in the energy storage capacitor, the microprocessoroperatively coupled to the transistor for controlling the transistor.16. The load control device of claim 8, wherein the microprocessor isoperable to place the communication circuit in an idle mode when theload control device is in the low-power mode.
 17. A load control devicefor control of the power delivered from an AC power source to anelectrical load, the load control device comprising: a controllablyconductive device adapted to be coupled between the AC power source andthe electrical load for controlling the power delivered to the load; amicroprocessor coupled to the controllably conductive device forcontrolling the controllably conductive device; a power supply adaptedto draw current from the AC power source through the electrical load forgenerating a DC voltage across an energy storage capacitor for poweringthe microprocessor; and a load circuit drawing current from the energystorage capacitor of the power supply; wherein the microprocessor isoperable to cause the load circuit to draw less current if the magnitudeof a voltage of the power supply drops below a predetermined threshold.18. The load control device of claim 17, wherein the load circuitcomprises an LED controlled by the microprocessor to provide visualfeedback.
 19. The load control device of claim 18, wherein themicroprocessor is operable to turn off the LED in response todetermining that the energy storage capacitor does not have enough timeto charge during each half-cycle of the AC voltage.
 20. The load controldevice of claim 18, wherein the microprocessor is operable to dim theLED in response to determining that the energy storage capacitor doesnot have enough time to charge during each half-cycle of the AC voltage.21. The load control device of claim 18, wherein the load circuitcomprises a plurality of LEDs controlled by the microprocessor toprovide visual feedback; wherein the microprocessor is operable to causethe LEDs to draw less current in response to determining that the energystorage capacitor does not have enough time to sufficiently charge. 22.The load control device of claim 17, wherein the load circuit comprisesa communication circuit.
 23. The load control device of claim 22,wherein the communication circuit is adapted to be coupled to an RFcommunication link.
 24. The load control device of claim 23, wherein themicroprocessor is operable to increase the sampling period of the RFcommunication circuit, such that the RF communication circuit wakes upless often to sample for RF energy.
 25. The load control device of claim22, wherein the microprocessor is operable to place the communicationcircuit in an idle mode in response to determining that the energystorage capacitor does not have enough time to charge during eachhalf-cycle of the AC voltage.
 26. The load control device of claim 17,wherein the load control device comprises a dimmer for controlling thepower delivered to a lighting load.